The present invention relates to an arc extinguishing circuit; and more particularly, relates to an arc extinguishing circuit capable of extinguishing arc discharges occurring within a glow discharge when used in a power supply circuit for generating a glow discharge.
Conventional glow discharge power supply circuits comprise a direct current (d.c.) voltage generating circuit, with a positive terminal and a negative terminal connected to the anode and cathode of the d.c. voltage generating circuit respectively. The negative terminal is connected to a target and the positive terminal is connected to a substrate holder. A substrate is then supported by the substrate holder so that the target and a surface of the substrate (hereinafter referred to as the xe2x80x9csubstrate surfacexe2x80x9d) face each other within a low pressure atmosphere. When the d.c. voltage generating circuit is then activated and a d.c. voltage is applied across the positive terminal and the negative terminal, a glow discharge is generated across the substrate surface and the target, the target is sputtered and a thin-film is formed on the substrate surface.
However, arc discharges can occur when certain kinds of abnormalities occur within the glow discharge. When arc discharging occurs, the target is sputtered in a localized manner and the thin film is unevenly formed on the substrate surface. Depending on the circumstances, this can be destructive to the thin-film formed on the substrate surface.
In order to resolve the aforementioned problems, it is the object of the present invention to provide an arc extinguishing circuit capable-of reliably suppressing arc discharges when used in a power supply for generating a glow discharge.
An arc extinguishing circuit of the present invention comprises a switch element equipped with a control terminal and two input/output terminals, with conduction across the two input/output terminals being based on a voltage inputted to the control terminal, a sense circuit, being a circuit having a primary winding and a voltage sense capacitor connected in series, with one end thereof connected to one input/output terminal and a remaining end thereof connected to the remaining input/output terminal and a secondary winding being magnetically coupled with the primary winding and having one end connected to the control terminal and a remaining end connected to one of the input/output terminals.
The arc extinguishing circuit of the present invention can also be configured in such a manner that when a trigger current flows in the primary winding, the voltage sense capacitor discharges due to the switch element conducting due to a voltage induced in the secondary winding, and a discharge current flows in the primary winding, with the discharge current flowing in the primary winding in the same direction as the trigger current.
The arc extinguishing circuit of the present invention can also have at least one inductance element, with one end of the inductance element being connected to one or both of the input/output terminals.
An arc extinguishing circuit of the present invention a switch element equipped with a control terminal and two input/output terminals, with conduction across the two input/output terminals being based on a voltage inputted to the control terminal, a sense circuit, being a circuit having a primary winding and a voltage sense capacitor connected in series, with one end thereof connected to one input/output terminal and a remaining end thereof connected to the remaining input/output terminal, a secondary winding being magnetically coupled with the primary winding and having one end connected to the control terminal and a remaining end connected to one of the input/output terminals, a resonant circuit, constituted by a resonant inductance element and a resonant capacitor connected in series, with one end thereof connected to one input/output terminal and a remaining end thereof connected to the remaining input/output terminal and a diode inserted across one or both of said one end of the resonance circuit and said one input/output terminal or said remaining terminal of the resonance circuit and said remaining input/output terminal.
The arc extinguishing circuit of the present invention can also comprise at least one inductance element, with one end of the inductance element being connected to a terminal of the resonant capacitor.
The arc extinguishing circuit of the present invention can also comprise a voltage limiting circuit connected in parallel with the voltage sense circuit and constructed in such a manner as to prevent a voltage across the terminals of the voltage sense circuit from rising above a fixed voltage when a voltage of a polarity which is opposite to a polarity in a steady state occurs across the terminals of the resonant capacitor.
An arc extinguishing method of the present invention comprises the steps of pre-charging a resonant capacitor while supplying a fixed voltage to a load from first and second output terminals in a steady state, when load impedance rapidly drops, sensing the rapid drop in impedance, causing a switch element connected across the first and second output terminals to conduct, short-circuiting the first and second output terminals, and discharging the resonant capacitor; causing the discharged current to flow through a resonant inductance, and causing the resonant capacitor and the resonant inductance element to resonate, generating a voltage, of a polarity which is opposite to the polarity generated in the steady state, at the resonant capacitor due to the resonance and putting the switch element into a non-conducting state using the reverse voltage and having the voltage across the first and second output elements revert to the steady state voltage.
The arc extinguishing method of the present invention can further comprise the steps of pre-inserting a diode element in the path of current flowing between the first and second output terminals via the switch element when the switch element is in a conducting state and the first and second output terminals are short-circuited and reverse biasing the diode element using a voltage generated at the resonant capacitor of an opposite polarity to the voltage generated in a steady state so as to halt resonance when a current flows between the first and second output terminals via the switch element.
The arc extinguishing method of the present invention can also comprise the steps of connecting a circuit constituted by the voltage sense capacitor and the primary winding connected in series across the first and second output terminals and pre-charging the voltage sense capacitor in the steady state and, when the load impedance falls rapidly, causing a current to flow in the primary winding due to discharging of the voltage sense capacitor, inducing a voltage in a secondary winding magnetically coupled with the primary winding, and putting the switch element into a conducting state using the voltage induced at the secondary winding.
The arc extinguishing method of the present invention can further comprise the steps of connecting a delay circuit to the voltage sense capacitor and increasing the time taken from commencing charging of the voltage sense capacitor until the voltage across both terminals of the voltage sense capacitor becomes the voltage across both terminals occurring in the steady state using the delay circuit.
In the present invention having the above configuration, both terminals of a d.c. power supply for generating a d.c. voltage are respectively connected to input/output terminals of a switch element, with the input/output terminals being taken as first and second output terminals, respectively, with each being connected to an electrode that is within a vacuum. The d.c. power supply is then activated with the electrodes separated from each other, a high voltage is applied across the electrodes and a glow discharge is generated. One electrode is connected to a target and the other electrode is connected to a substrate. When the target and substrate are arranged in such a manner as to face each other, the target material is sputtered by the glow discharge and a thin film is formed on the substrate surface.
The present invention also has a voltage sense circuit constituted by a voltage sense capacitor and a primary winding connected together in series. When the voltage sense capacitor is pre-charged in a steady state and an arc discharge then occurs as the result of some kind of abnormality so that the potential difference across the first and second output terminals drops rapidly, a discharge current is supplied from the voltage sense capacitor to the primary winding and a voltage is induced at the secondary winding magnetically coupled with the primary winding.
When the voltage sense capacitor is pre-charged to a voltage of an appropriate value and a voltage is induced at the secondary winding, the switch element in a non-conducting state connected across the first and second output terminals can be put into a conducting state, the first and second output terminals are short-circuited, the electrodes are short-circuited and arc discharges can be extinguished. As arc discharges can be extinguished a short time after occurring, the quality of thin films formed on the substrate surface does not deteriorate.
The arc extinguishing circuit of the present invention is configured in such a manner that when a trigger current flows in the primary winding, the switch element conducts due to the voltage induced at the secondary winding so that when the voltage sense capacitor discharges, a discharge current flows in the primary winding in the same direction as the trigger current.
By adopting this kind of configuration, the discharge current flows in the same direction as the trigger current that causes the switch element to conduct. The conducting state of the switch element is therefore maintained while the discharge current is flowing and is maintained until discharge of the voltage sense capacitor is complete.
Furthermore, in the present invention, an inductance element is provided, with one end thereof being connected to one or both of the input/output terminals.
In this case, the current flowing between the electrodes can be limited by the inductance element even when arc discharges occur due to an abnormality and a large current flows between the electrodes, and the potential difference across the electrodes can be rapidly reduced. Therefore, when an arc discharge occurs, the pre-charged voltage sense capacitor is discharged, the switch element is made to conduct by the discharge current and the arc discharge can be extinguished.
A further arc extinguishing circuit of the present invention has a resonance circuit. With this configuration, the voltage sense capacitor and the resonant capacitor are pre-charged in the steady state. When an arc discharge occurs in this state, the switch element conducts so that the output terminals are short-circuited, the resonant capacitor discharges, the discharge current flows through the resonant inductance, and the resonant capacitor and the resonant inductance element resonate. A voltage of a polarity opposite to that occurring in the steady state is therefore generated at the resonant capacitor due to this resonance and the switch element is therefore put into a non-conducting state.
As an example, if a diode element is inserted beforehand in the path of current flowing between the first and second output terminals via the switch element when the first and second output terminals are short-circuited, when a current flows between the first and second output terminals, the diode element is reverse biased by the voltage occurring at the resonant capacitor of a polarity opposite to that which occurs in the steady state and the switch element is therefore put into a non-conducting state.
In this case, a non-conducting state can be entered before the voltage sense capacitor has finished discharging. The time until the switch element returns to a non-conducting state can therefore be made short and the time taken to return to a steady state after extinguishing an arc discharge can also be made short.
When a resonance circuit is provided in this way, if the reverse voltage occurring due to the resonance becomes too large, directly after the first and second output terminals are short-circuited and the arc discharge is extinguished, the voltage across the first and second output terminals rises excessively and again becomes a voltage at which arc discharges become possible so that arc discharges may occur again.
Therefore, in the present invention a voltage limiting circuit is connected in parallel with the voltage sense circuit. In this case, as it is possible to ensure that the voltage across the first and second output terminals does not rise above a prescribed voltage, the voltage across the first and second output terminals can be made so as not to rise as high as a voltage at which arc discharges are possible by setting the prescribed voltage to an appropriate value. It can therefore be ensured that arc discharges do not occur again directly after the first and second output terminals are short-circuited.
Further, according to an arc extinguishing method of the present invention, first and second output electrodes are each connected to one electrode that is within a vacuum, and when a d.c. power supply is turned on with each electrode placed apart from the other electrode, a high voltage is applied across the electrodes and a glow discharge is generated in a steady state.
When an arc discharge then occurs due to some kind of abnormality and the impedance across the electrodes falls rapidly, this abrupt fall is sensed, a switch element connected across the first and second output terminals is put into a conducting state, the first and second output terminals are short-circuited and the electrodes are short-circuited so that the arc discharge can be extinguished.
The switch element is made to conduct and the arc discharge is extinguished, the resonant capacitor pre-charged in a steady state is made to discharge, the current discharged flows through the resonant inductance and the resonant capacitor and resonant inductance element resonate. A voltage of a reverse polarity to that generated in the steady state is therefore generated at the resonant capacitor, the switch element is put into a non-conducting state by the reverse voltage and the steady state is made to return.
In the arc extinguishing method of the present invention, the configuration may be such that a circuit constituted by a voltage sense capacitor and a primary winding connected in series is connected across the first and second output terminals and the voltage sense capacitor is pre-charged in a steady state. When the load impedance then falls rapidly, a current flows in the primary winding due to discharging of the voltage sense capacitor, a voltage is induced in the secondary winding magnetically coupled to the primary winding and the switch element is put into a conducting state by the voltage induced at the secondary winding.
With this configuration, abrupt falls in load impedance are sensed using discharging of the voltage sense capacitor, the discharge current flows through the primary winding and the switch element is made to conduct. The first and second output terminals are therefore short-circuited and it is possible to extinguish arc discharges.
With the arc extinguishing method of the present invention, a delay circuit is connected to the voltage sense capacitor and the time from charging of the voltage sense capacitor being started to the voltage across both terminals reaching that of the steady state is lengthened using this delay circuit.
By adopting this kind of configuration, the voltage induced in the secondary winding as a result of current flowing in the primary winding due to the voltage across the terminals of the voltage sense capacitor is prevented from reaching a voltage at which the switch element can enter a conducting state before the voltage across the first and second output terminals reaches the voltage occurring in a steady state where a glow discharge is possible.
Therefore, before a glow discharge is generated, when the state is such that an arc discharge is possible, it is ensured that it is not possible for the switch element to erroneously conduct, resulting in a short circuit across the first and second output terminals to short circuit; and a glow discharge can therefore be generated in a reliable manner.